1. Field of the Invention
The present invention relates to a single device for the adjustment of the maneuver forces of movable members of an aircraft via a control part acting on two independent, linear control links or chains.
Although not exclusively, the device in accordance with the invention is more particularly intended for the control of the cyclic plate of a helicopter rotor. In this case, the movable members then correspond to connecting control rods, jacks or similar, which are connected to the cyclic plate and which make it possible to obtain, in a known way and as a function of the displacements imposed by the pilot on the device, by acting on a column known as a cyclic column, the inclination of the cyclic plate around two perpendicular axes, which inclination of the cyclic plate then controls the tilting of the attitude of the rotor following the angular displacement of the column by the pilot.
However, the device could also be applied to the control of aerodynamic surfaces of an aircraft. In this case, the movable members correspond, for example, to the elevators and warping surfaces pivoting around transverse axes, which are controlled in a co-ordinated way by a control column or a "horn steering wheel" arranged at the upper end of a lever which moves longitudinally.
2. Prior Art
Numerous devices for the control of movable members of an aircraft are already known, such as that taught by French Patent FR-764 635 and applied to the control of the inclination of a rotor.
Generally, the known devices comprise a pivoting control column to which are articulated a shaft and a connecting rod. Under the action of an angular displacement of the column in a first plane, the shaft may pivot around its axis and give rise, by the intermediary of a first link, to the displacement of at least a first movable member. By analogy, under the action of an angular displacement of the column in a second plane, the connecting rod can be displaced in translation parallel to its longitudinal axis and can give rise, by the intermediary of a second link, to the displacement of at least a second movable member.
Hence, in the preferred application of the device to the control of the cyclic plate of the rotor of a helicopter, it is known that the displacement of the first member articulated to the cyclic plate gives rise to the pivoting of said plate around an axis chosen such that, having regard to the gyroscopic precession effect, this pivoting of the cyclic plate brings about a forward or a rearward inclination of the rotor disk, according to the direction of the angular displacement of the cyclic column in the first plane defined by the roll axis and the yaw axis of said helicopter. As for the lateral inclination of the rotor disk parallel to the roll axis of the helicopter, it is obtained by the opposite displacement of two movable members, connected to the plate and arranged respectively symmetrically, diametrically opposing, on either side of the axis which corresponds to the longitudinal tilting of the rotor disk. The angular displacement of the cyclic column in the second plane, defined by the pitch and yaw axes, then brings about the tilting of the rotor to the right or to the left according to the direction of the angular displacement of the column. These angular displacements of the column forwards or rearwards and to the right or to the left may be combined in such a way as to permit all the possible tiltings of the rotor according to the flight conditions demanded of the helicopter.
In addition, these control devices are also provided with friction means which, on the one hand, permit the pilot to apply the correct force during angular displacements of the cyclic column, and, on the other hand, make it possible to provide an adjustable braking of the angular displacements of the column under the forces originating from the cyclic plate, in particular in order to filter out the dynamic forces reaching the pilot, thereby improving the comfort and precision of piloting.
In a first embodiment, such as described in Patent FR-764 635 and used, for example, on numerous light helicopters, the friction means comprise two independent mechanisms with an adjustable knurled wheel interacting with a slide, the clamping of the knurled wheel against the slide determining the friction between these latter desired by the pilot. One of the two mechanisms is provided for the angular displacement of the column pivoting in the first plane, while the other mechanism is provided for the angular displacement of the column pivoting in the second plane. Although this first embodiment of the friction means is mechanically simple and offers a possibility of independent adjustments between the two mechanisms, on the other hand, it entails numerous drawbacks. First of all, the pilot is constrained to adjust the two knurled wheels in order to adapt the friction to his wishes. Moreover, these friction means lead to uncomfortable and imprecise piloting. In fact, the force to be overcome for any displacement of the cyclic column combining an angular displacement in the two planes (that is to say at any instant) is equal to the sum of the longitudinal force and of the lateral force to be provided. Moreover, the direction of this combined force is never aligned with that of the movement, which, on top of the unergonomic character of the movement supplied by the pilot, is translated, on helicopters equipped with these friction means, into the impossibility of performing accurate curved trajectories which are then carried out in a "jerky" fashion, by following, as well as possible, said curved trajectories to be executed.
In a second embodiment, the friction means of the control devices use a hemispherical ball joint at the base of the cyclic column, serving for the pivoting of the column, in order to obtain the desired friction according to the displacement of the column. In order to do this, the ball joint comprises a fixed friction dish solidly attached to the floor and traversed by the column, and a friction dish linked to the column and applied against the fixed dish. A knurled knob, surrounding the column, allows adjustment of the friction between the two dishes.
Hence, by virtue of these ball joint friction means, the adjustment of the friction of the column is obtained by a single knob, and the force to be delivered by the pilot is then tangential to the movement imposed by the pilot, removing the abovementioned drawbacks.
Nevertheless, these ball joint friction means cause other drawbacks to appear. First of all, it turns out that embodiment is mechanically complicated and tricky. Furthermore, by reason of the axial passage of the column in the hemispherical dishes, the friction is not symmetric during any displacement whatever of the column. Moreover, as the ball joint is situated in the vicinity of the floor of the helicopter, it rapidly gets dirty and the adjustment knob of the friction means, which is accessible to the pilot, then becomes practically inaccessible for the co-pilot. It is then necessary to install another on the lower part of the co-pilot's column, but then the simultaneous adjustment of the two devices by the pilot and by the co-pilot is difficult. Furthermore, the force to be supplied by the pilot for a longitudinal displacement of the column (forwards or rearwards) is the same as that which it has to deliver for a lateral displacement (to the right or to the left), which is unergonomic. In fact, it is easier for a pilot to exert a higher longitudinal force forwards or rearwards than a lateral force to the left or the right.